Technical Field
The present invention relates to a method of calculating a circumference used when bevel edging is applied to a spectacle lens, a method of manufacturing a spectacle lens, and a circumference calculating device and a circumference calculating program.
Description of Related Art
A spectacle lens framed into a spectacle frame is formed by being subjected to an edging process applied to an uncut lens. An edging process includes “edging” for cutting and polishing the uncut lens so as to match a spectacle frame shape, and “beveling” for providing a bevel on an edged lens. When such an edging process is performed, the following situation should be prevented: namely, a lens is not framed into a spectacle frame due to an excessively large spectacle lens after edging, or a gap is generated between the spectacle lens after edging and the spectacle frame. In view of this point, conventionally a bevel circumference of the spectacle lens after edging is measured so as to match the circumference of the spectacle lens, and defect and non-defect of this spectacle lens is judged (for example, see patent documents 1 and 2), and the bevel circumference is set in a case that beveling is performed so as to match the circumference of the spectacle frame (for example, see patent documents 3 and 4).    Patent document 1: Patent Publication No. 3075870    Patent document 2: Patent Publication No. 3904212    Patent document 3:    Japanese Patent Laid Open Publication No. 1999-052306    Patent document 4:    Japanese Patent Laid Open Publication No. 2002-018686
Incidentally, when the beveling is performed to the uncut lens, an interference occurs during beveling between a beveling tool and a beveled place of the lens even at a point other than a theoretical cutting point, under an influence of a lens shape to be edged, a lens curve to be edged, and a diameter and a bevels shape of the beveling tool (cutting and polishing tool) used for the beveling, and tapering or strain, etc., is probably generated in the shape of the formed bevel. For example, a position of the beveling tool is not required to be varied in Z-axis direction unless a locus of a bevel tip in a circumferential direction (called “bevel tip locus” hereafter) is varied in the Z-axis direction (lens optical axis direction). Therefore, the tapering or the strain, etc., of the bevel shape is not generated. Meanwhile, the lens has a curve based on a prescription content, and has a variation in the bevel tip locus in the Z-axis direction in most cases. Accordingly, when the beveling is performed, the tapering or the strain, etc., is generated in the shape of the formed bevel due to the interference between the beveling tool which is displaced in the z-axis direction, and the beveled place of the lens, resulting in a situation that the bevel is not positioned at an expected position when the beveling is performed.
However, the situation that the tapering and the strain, etc., is generated in the bevel shape under the influence of the beveling tool, is not taken into consideration in a conventional technique disclosed in patent documents 1 to 4. Namely, even in a case that the tapering or the strain, etc., is actually generated in the bevel shape under the influence of the beveling tool, the bevel circumference in a case of not generating the interference, is selected as a reference. Accordingly, if the tapering or the strain, etc., is generated in the bevel shape, a deviation is generated between an expected bevel circumference and an actually obtained bevel circumference, and whether or not indicated beveling is performed, cannot be accurately judged from the actually obtained bevel circumference, which probably invites a finish size failure of the bevel edging as a result. Such a size failure is also a factor of inviting a situation that even if the beveling is performed so as to match the circumference of the spectacle frame, the spectacle lens after beveling cannot be correctly fitted into the spectacle frame. Therefore, the generation of the size failure should be prevented.
Accordingly, an object of the present invention is to provide a method of calculating a circumference, a method of manufacturing spectacle lens, a circumference calculating device and a circumference calculating program capable of improving a fitting ratio of a spectacle lens after beveling into a spectacle lens frame, and realizing a supply of a beveled spectacle lens with a stable good quality.